As professional in-home and virtual personal trainers, we field plenty of questions about diet. One of the most popular diet trends the Nielsen Fitness team is asked about is intermittent fasting. In fact, intermittent fasting is “one of the world’s most popular health and fitness trends. Some people claim it’s helped them lose weight, improve their health, and simplify their lifestyles” (Healthline, 2024). But is it right for you? More importantly, is it a good option in the long run? In this post, we’ll discuss the basics of intermittent fasting and the science behind the method.

THE ORIGIN OF INTERMITTENT FASTING

Humans have been fasting since the beginning of time, so it’s nothing new for the body. For centuries, fasting has been practiced for religious reasons or during times of food scarcity. Today, some alternative systems of medicine even use fasting for therapeutic purposes. As a result, our bodies have adapted to handle extended periods without food.

THE BASICS OF INTERMITTENT FASTING

At its core, intermittent fasting (IF) is a basic concept. The idea is to fast for a set amount of hours before consuming calories during a scheduled eating window, then repeat the process once that window closes. For example, 16:8 is a popular approach that requires a 16-hour fast before an 8-hour eating window. Whether that eating window is between 8 AM and 4 PM or 12 PM and 8 PM is up to you; the hours are set around your schedule and what suits your lifestyle.

Other popular fasting ratios are 14:10 and 5:2. However, 5:2 is slightly more complicated. “In a 5:2 diet, you eat “normally” five days out of the week. These are your non-fasting days. The other two days are fasting days. You consume fewer calories on those days depending on your sex: 500 calories for women, 600 calories for men” (Cleveland Clinic, 2024).

In reality, IF is more of an eating pattern rather than a set diet, as the technique does not specify what foods should or should not be consumed during eating windows. It’s also important to note that most IF approaches allow zero-calorie liquids like water, black tea, and black coffee to be consumed during fasting.

THE INTENTION OF INTERMITTENT FASTING

There are a few different intentions behind IF, depending on your goals. For those living with health conditions like hypertension or diabetes, fasting has been shown to lower health risk factors by reducing blood sugar levels and bad cholesterol. For those interested in weight control, IF can aid in reducing the amount of calories you consume in a 24-hour window. There’s even science that suggests fasting improves mental function. “When you fast, your body has less toxic materials flowing through the blood and lymphatic system, making it easier for you to think. While fasting, the energy you’d normally use to digest food is available to be used by the brain” (Web MD, 2024).

FASTING AND EXERCISE

Aside from the reduction of risk factors for diabetes and other long-term health conditions, “fasting workouts may enhance weight loss and other benefits of fasting. However, the adverse effects of exercising on an empty stomach may affect the results of your workouts” (Very Well Health, 2024).

Exercising while fasted can encourage your body to burn more fat as fuel, as carbohydrates (your body’s preferred source of energy) are not readily available. However, if you’re training at a high intensity for an extended period, your body may begin to breakdown muscle to generate glucose. This is the opposite of what you want when training to improve body composition and boost longevity. Training on an empty stomach can also affect your mood, which is a direct result of IF’s effect on blood sugar.

INTERMITTENT FASTING FOR WOMEN VS. MEN

One of the biggest problems with IF is the fact that most studies have been conducted without attention to female health and fertility. Despite the popularity of IF, “its effects on female reproductive hormones and menstrual cycle regulation remain an area of growing scientific inquiry. While the metabolic benefits of IF, such as improved insulin sensitivity, reduced oxidative stress, and cardiovascular health, are well documented, concerns have been raised regarding its impact on hormonal balance and reproductive function in women. Unlike male physiology, which appears more resilient to fasting-induced hormonal fluctuations, the female endocrine system is intricately linked to energy availability, making it particularly susceptible to dietary modifications” (The International Journal of Medical Science and Health Research, 2025). Prolonged fasting in women could contribute to cycle irregularity, inflammation of the gut microbiome, and disruption of circadian rhythm.

OUR INTERMITTENT FASTING TIPS

The first thing any of our in-home and virtual personal trainers will tell you about diet is that – just like exercise – there’s no quick fix or magic trick to help you lose weight or gain muscle. IF is a tool that can sometimes aid your health and fitness goals, but it must go hand in hand with regular physical activity and smart food choices.

The most important thing is that you’re moving every day and eating a balanced intake of protein, carbs, and fats that support a strong, healthy body. If you’re new to the world of fitness, an in-home or virtual personal trainer can help guide you to make the choices that work best for you. It’s also important to speak to your doctor before beginning any new diet or training regimen, especially if you have a health condition.

FINAL WORDS

Trends come and go, but intermittent fasting goes well beyond a buzzy diet or fitness fad. It’s rooted in a long history of the body training to support itself in times of need. That said, it’s not a technique that’s appropriate for everyone. If you’re curious about whether or not IF is ideal for you, talk to your doctor or book and appointment with a team member at Nielsen Fitness to start asking questions! Our in-home personal trainers are available in Toronto, Collingwood, London, Hamilton, and Ottawa, with virtual personal trainers available everywhere!